The objectives of the proposed research are to define the role of enterotoxic substances produced by non-invasive enteropathogenic Escherichia coli strains in the pathogenesis of diarrhea caused by E. coli, to develop techniques for their recognition and to develop, experimentally, information which will lead to rational methods of control such as by immunization. To these end, we propose to continue our efforts to obtain homogeneous preparations of E. coli enterotoxins of high specific activity and to characterize the products by physical, chemical and immunologic criteria. Attempts will be made to investigate their role in the production of immunity against challenge with homologous and heterologous E. coli strains and toxins and to define further the interrelationship between E. coli and cholera enterotoxins. Fermentor-grown culture supernatants will be concentrated by gentle physical procedures and fractionated by gel filtration, ion exchange chromatography, electrophoresis and immunoaffinity chromatography. Biologic activity will be assayed in ileal loop models, skin tests, and in tissue culture systems. Products of interest will be tested as immunizing antigens by systemic and peroral routes after inactivation by chemical means, if necessary. Attempts will be made to develop in vitro tests for recognition of enterotoxin and its specific antibody.